compiler-rt/libcxx: Use clang as compiler

(From OE-Core rev: e75b2dee39fc0a35f764caa6b72af2a0b9beb165)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/clang/compiler-rt_git.bb

@@ -58,6 +58,8 @@ BUILD_CXX = "${CCACHE}clang++ ${BUILD_CC_ARCH}"
 LDFLAGS += "${COMPILER_RT} ${UNWINDLIB}"
 CXXFLAGS += "${LIBCPLUSPLUS}"
 
+TOOLCHAIN = "clang"
+
 def get_compiler_rt_arch(bb, d):
     if bb.utils.contains('TUNE_FEATURES', 'armv5 thumb dsp', True, False, d):
         return 'armv5te'